The present invention relates to a back-light device particularly suitable for being applied to a transmissive liquid crystal display apparatus, and a liquid crystal display apparatus.
Recently, a display device made considerably thin such as an LCD (Liquid Crystal Display), PDP (Plasma Display Panel) and the like is proposed and commercially available as the display device replacing a CRT (Cathode Ray Tube) for a television receiver. Particularly, since an LCD apparatus using an LCD panel is capable of being driven by low power consumption and a large-sized LCD panel has become capable of being manufactured at low costs, the LCD apparatus using an LCD panel has been widely used and the technical research and development is advanced.
The above LCD apparatus mainly uses a backlight system in which a color image is displayed by a backlight device that illuminates the whole rear surface of the transmissive LCD panel including a color filter from a rear side.
A CCFL (Cold Cathode Fluorescent Lamp) which emits white light by using a fluorescent tube and an LED (Light Emitting Diode) are considered to be promising as a light source of the backlight device (refer to Patent Document 1, for example).
Particularly, with development of a blue LED, respective LEDs of emitting red light, green light and blue light that are three primary colors in light are prepared, and white light with high color purity can be obtained by mixing red light, green light and blue light emitted therefrom. Therefore, with those LEDs being a light source of the backlight device, color purity through an LCD panel becomes high and so the achievable color gamut can be greatly expanded in comparison with a CCFL. Further, luminance of the backlight device can greatly be improved by using an LED chip of high power.
As described above, in the case in which an LED is used as the light source of the backlight device, when the LED is arranged directly under the light-emitting surface, namely, when a direct type LED is employed, brightness and color uniformity may be worse because the LED is a point source of light.
As a method to solve the above problem, it is conceivable to enlarge the distance between the LED and a diffusion plate, however, as a result, the thickness of the backlight may become extremely large in comparison with the backlight using a CCFL. Further light weight and thin shape have become indispensable in the LCD apparatus and the further thin shape is desired also in the backlight.
Then, as a method to decrease the thickness, a structure is proposed in which a light-guiding plate is used to make light from the light source arranged at a part of the plate reflect multiple times to obtain a surface light source. In other words, the light-guiding plate is used to make the backlight thin and to improve the uniformity of brightness.
Patent Document 1: Published Japanese Patent Application No. H8-136917.